# SVC_WaitVBlankIntr

## C Specification

      #include <nitro/os/common/systemCall.h>

      void SVC_WaitVBlankIntr( void );

## Description

Continues to wait in a `Halt` status until a V-Blank interrupt is generated

Set the V-Blank check flag with `OS_SetIrqCheckFlag( OS_IE_V_BLANK )` in the V-blank interrupt handler. `SVC_WaitVBlankIntr()` checks whether or not this flag has be set after IRQ interrupt and whether V-Blank has already occurred.

When multiple threads are used at the same time, the overhead for the system call can be reduced in comparison to repeatedly calling `OS_Halt()`.

If `SVC_WaitVBlankIntr()` is called for the same interrupt at the same time for multiple threads, be aware that only one thread can be restored for each corresponding V-blank.

## Argument

None.

## Return Values

None.

## See Also

`OS_SetIrqCheckFlag, OS_Halt`

## Revision History

11/02/2004 Deleted description of `SVC_WaitIntr()`
04/22/2004 Added caution for using with multiple threads.
01/18/2004 Initial Version